Method and means for signaling



Jan. 8 1924. 1,480,217

- J. MILLS v METHOD AND MEANS FOR SIGNALING Original Filed Dec. 29, 19162 Sheets-Sheet 1 lwvehbr: i/0/7/7 /V///s.

ky my Jan; 8 1924.

J. MlLLS METHOD AND MEANS FOR SIGNALING 2 Sheets-Sheet 2 Original FiledDec. 29, 1916 Patented Jan. 8, 1924. I

UNITED. STATES PATENT OFFICE.

JOHN MILLS, OE WYOMING, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COM-PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

METHOD AND MEANS FOR SIGNALING.

Substitute for application Serial No. 139,541, filed December 29. 1916.This application filed January 20,

1922. Serial No. 580,528.

to either wire or wireless telephone commu-.

nication in which it is desirable to prevent an intelligibleinterception of the signal transmitted.

The present application is a substitute for applicants copendingapplication Serlal No. 139,541 filed December 29, 1916.

An object of. the invention is to send the signal in such a form that itwill be unin-' telligible when received by ordinary appa ratus and toclarify the signal at the proper receiving station by specially providedmeans.

This is accomplishedby superposing, on

the outgoing talkor signal currents, a complex noise formed by. currentsof several frequencies lying\ in the most important part of the voicefrequency range. To"

clarify the signal at the proper receiving station, the inventionprovides for thesuperposition upon the incoming talk and its combinednoise of a complex noise simllar to the noise originally superimposedbut ex actlv opposite in the phase of all itscomponents. The noise isthus suppressed from the signal which may be recelved free fromconfusion.

Another object of the invention is to provide a source of noise orconfusion currents suitable for maskingthe signal currents to be.transmitted. This is accomplished by impulsively exciting anoscillatlon network having several degrees of freedo m i. e., severalperiods of free vibration, w1th1n the 5 voice frequency range. Thlsnetwork when iinpulsed serves as a source of currents of variousaudio-frequencies correspondlng to the periods of free vibration of thenetwork. Another object of the invention. is to maintain the confusioncurrents generated at the receiving station in phase opposition to theconfusion currents arriving at the receiving station from the sendingstation. To this end the invention provides an oscillation network ateach station for supplying the confusion currents and both net? worksare energized by the same source of current and hence each networkresponds in a like manner to variations in the character of the suppliedcurrent. Interposed between the source and the network at the receivingstation is provided a. phase adjusts .and these two currents will alwaysbe main- In carrying tained in phase opposition.

out the invention various novel combinations of apparatus and methodshave been utilized. v

For example 'there has been provided a receiving station in whichreceivedwaves are successively utilized to produce waves of otherfrequencies. Interposed between the various stages of frequency changingmeans are one or more means serving for amplification, selection of oneor more components of the resultant waves, and mi directionalconduction. The thermionic type of repeater conveniently serves both asan amplifier and as a unidirectional conduc-' tor. The purpose of theunidirectionally conducting means is toprevent backward reaction throughthe. circuit.

The principles of the invention are ob-v viously, applicable in numerousmodified forms of systems.

Forfurther particulars of the invention reference may be made to thedrawings, in which Fig. 1 shows diagrammatically: an embodiment of theinvention; and Fig 2 illustrates a modification.

To aid in reading the drawings, the thermionic repeaters have beenprovided with an auxiliary reference letter to indicate the function theaudion performs, i. e.,; A:amplifier, Gzgenerator Pzcurrent limitingdevice.

In Fig. 1 the sending station X and the receiving station Y are in radiocommunication although these stations may be connected by a wire line ifdesired. At the sending station X, the generator 4 is adapted I tosupply control oscillations of a frequency near the limit of audibility,for instance, a

frequency of thirt cycles which is adj acent' than 30 cycles for examplecycles. In

such a case a mechanical generator might be I preferred to the generator4 on account of the technical difliculties to be surmounted in makingvacuum tube generators of such low ,frequencies as 5 cycles per second.The

generator 4, which may be of any suitable type is adapted to energizethe line 3 through the two current paths 5 and 6, the former beingcoupledto the generator 4 by means of the coil 7 and the latter by meansof the coil 8. The current path 6 comprises a current limiting device 9.The input circuit of the current limiting device 9 is tuned.

by means of condenser 51 to the frequency of the control oscillationssupplied by generator 4. The current limiting device 9 comprises avacuum tube 10.of the audion type having a resistance 11 in its outputcircuit. When the' current in the output circuit reaches a certain highvalue, the voltage drop across resistance 11 becomes large enough toprevent further increase in the current, which accordingly has, a flattop or complex wave form. Coupled with the current limiting device 9 areone or more amplifiers '12 of well known type, by means of whichamplified currents having a com lex or flat top wave form maybe supplito the oscillation network or sectional loaded artificial line 13. IThis network may be made in any desired number of sections, the numberhere-shown being four. An electromotive impulse supplied by theamplifier 12 to the oscillation network 13 will set up in this network anumber of free oscillatlons equal to the number of sections of thenetworkand the frequencies ofwhich are deter-. mined by the constants ofthe circuit.

For the purposes of this invention, the inductance and capacity elementsin each section of the network 13 are chosen to give four frequencieswhich extend throughout the voice frequency range, that is, frequenciesof 100 to 2000. By way of example it may be'cited that ifthe resistance,inducthe tance and capacity of each section have values: R=negligible ascompared to L202 henry, C 0.128 m. f., then the four frequenciessupplied .by this network will have the Values f :780, f :l170, f=1620,'

71-:1960. The currents delivered by the network 13 will hereafterbe'known as noise currents orconfusion currents as they are.

- by means of condenser 55 to the frequency of the control oscillationssupplied by generator 4. The amplifier 17 in the current path 5 and thevarious audion elements shown in the current path 6 are unilaterallyconductive, whereby energy is delivered from'the generator 4 to the line3, but one of these current paths is prevented from sending currentthrough the other of these paths. transmitted is transferred to the line3 by means of the conventional transmitter circuit 19. It will beobserved that the network 131is selected with such values of inductanceand capacity that the two middle sections will constitute a wave filterhaving a cut-off limit at about the frequency of 2,000 cycles persecond. Any disturbances introducedby the power limiting device 9 orother elements in the path 6 which are higher than this frequency willbe attenuated in the network 13 due to its action as a low pass filter.

At the sending station X, the line 3 has superposed thereon signalingcurrent from the circuit 19, confusion currents by means of thetransformer 16 and control currents from the current path 5. If thisline 3 were connected to an ordinary receiver, the combined signal andconfusion currents would be translated into the original signal whichwould have superimposed a complex noise which would mask the signal andrender the same unintelligible. The currents the line 3 are utilized tomodulate, by means of any suitable modulator M, the carrier currentssupplied by a suitable source G. The modulated currents sent fromantenna 52 are received by antenna 53 where they are selected by meansof any suitable detector D which supplies the detected currents to line54. If a receiver is connected to line 54 the signal will be confused inthe same manner as if the receiver L I is connected to the line 3. Inorder that the signal originating in circuit 19 may be received freefrom confusion at the proper receiving station Y, confusion currents ofopposed phase to those'supplied by the transformer 16 are combined withthe superimposed confusion and signal currents received at that station.

At the station Y, the line 54 is connected to the signal or othertranslating circuit 20 through the paths 21 and 22. In the path 21, theamplifier 56 serves to increase the amplitude of all of the incomingcur- The telephonic speech signal to be suppressed by means of thefilter 23 so that the transformer 24 serves to impress amplified signaland confusion currents to the circuit 20. The input end of current path22 is tuned to the frequency of the control oscillations by means of thecondenser 25. The control oscillations selected by the tuned circuitcomprising the condenser 25 and the inductance 26 are supplied to theamplifier 27 which is coupled to a tuned circuit 28 which is also tunedto the frequency of the control oscillations. By means of the adjustableresistance R, inductance L and capacity C, the phase of the controloscillations supplied to the transformer 29 is adjusted so that the twocurrent paths 21 and 22 supply the signal circuit 20 with confusioncurrents .which are opposed in phase. The control currents, which areproperly adjusted in phase by means of L, R and C, are supplied to thepower limiting device 30 which is similar to the power limiting device 9above described. The currents having a flat top or complex'wave formsupplied by the device 30 are impressed on the oscillation network 31,filter 32 and amplifier 33, which are similar to the oscillation network13, filter 14 and amplifier 15 at the station X. The superposedconfusion and signal currents supplied by a transformer 24 are combinedwith the opposite phase confusion currents supplied by the amplifier 33,whereby the confusion currents originally superimposed are suppressedand the signal currents are received in the circuit 20 free from con-'fusion.

In the modified form of sendin station shown in Fig. 2, instead of usinga generator such as 4 to continually supply the 4 control oscillations,these oscillations are generated by means of the .voice currents sothat, upon the cessation of the voice cur-v rents, the generation of thecontrol oscillations will also cease and no current will be transmittedover the line ,3. This method of generating control currents is morefully described and claimed in applicants copending application SerialNo. 124,958, filed October 11, 1916. The current paths 5' and 6 areidentical with the corresponding paths 5 and 6 shown in Fig. 1.Inductively related with the coils 34 and 35, which, are traversed bythe signal currents, is the .coil 36 which transfers the speech currentsto the amplifier 37, the output circuit of which is tuned by means ofthe condenser 38. to the control frequency. The control oscillations maybe further amplified by means of the amplifier 39 and supplied by meansof the coil 40 to the coils 7 and 8. The coils 34 and 35 are included inthe input circuit of a vacuum tube 41, which is essentially unilaterallyconducting, in order to prevent a local circulation of power from eitherof the paths 5 and 6' through. the control current path136, 37, 38, etc.

, It is-proposed to change from time to time, the character of theconfusion cur rents transmitted by changing the values of the capacityor inductance in the sections of the network, the receiving stationhaving its network correspondingly changed.

The novel features believed to be inherent in the invention are definedin the appended claims.

What is claimed is:

1. The method of secret telephony which comprises generating currentsrepresenting speech, generating confusion currents, having at least onefrequency coinciding with the'frequency range of said first mentionedcurrents, transmitting simultaneously and together the superposed speechand confusion currents, and receiving -a relatively wide band offrequencies of the speech representing currents free from the confusioncurrents.

2. The method of secret telephony which consists in generating speechrepresenting currents, generating confusion currents having a frequencycomponent within the range of audible frequencies to be received,simultaneously superposing and transmitting together the speech andconfusion currents, eliminating the confusion currents at the receivingstation and receiving thereby a relatively wideband of the essentialspeech frequencies free from the confusion current component within thedesired range.

3; The method of secret signaling which consists in superposing'confusion currents having frequencies within the range of 200 to 2,000cycles per second upon the outgoing talk tablishing the desired phasedifference be-' tween said currents, and maintaining said phasedifference constant by supplying the currents at both of said stationsfrom a common source of frequency other than the frequency of saidcurrents.

5. The method of secret signaling which consists in generating (onfusioncurrents from control currents, transmitting the control, confusion andsignal currents to a distant station, generating other confusioncurrents from the control currents received 7 at said station, adjustingthe phase of said other confusion currents and in combining from theproduced waves, means for pro ducing amplified waves of the selectedfre- 13 quencyrange, means for producing from theamplified waves otherwaves of changed frequency, means for selecting from the other waves ofchanged frequency alternatin current waves of a frequency range di erentfrom the received waves and different from the first named selectedwaves, means for producing amplified waves of the frequency range lastselected from the selected waves, and a utilization circuit for theamplified waves energy thus produced whereby the energy 'level in eachamplifying device is kept small, whereby each amplifying device isprevented from being loaded wit-h undesired energy, and whereby singingis pre- 30 vented by the operation of the selective means preceding eachamplifying device in attenuating currents of frequencies which are notattenuated by the selective means preceding the other amplifying device;

35 7. The method of transmission which comprises modulating a carrierwave in accordance with a signal wave and in accordance with at leasttwo'control waves of-different frequencies, and controlling a oo- 40operating receiver by the conjoint action of the control waves.

8. The method of secret signaling which comprises superposing confusioncurrents of more than one frequency on the speech ourrents to betransmitted, simultaneously transmitting the superposed speech. andconfusion currents and in receivingthe speech currents free from theconfusion currents.

9. A high frequency transmission system comprising a modulator and aninput source of waves for said modulator, said source comprising intandem electrical elements having definite upper and lower cut-ofi"limits whereb the waves transferred to said modulating evice from saidsource are limited to a. definite band or frequency range.

10. The method of masking a talking signal which consists inperiodically superimposing upon and transmitting with said signal,trains of electric waves having several frequencies located throughoutthe range of audibility. -1

11. The method of renderin a talking 08 signal unintelligible whichconsists in auto- 1,4so,217 Y causingthe control current variations toeliminate the confusion current at a receiving station. 14. A signaltransmitting system including a generator of control currents, anoscillation network, means whereby said generator causes confusioncurrents having frequency components other than the control currentfrequency to be generated in said network, and means for transmittingthe confusion current and. the control current simultaneously.

15. A system for--generating noise currents comprising the combinationof a source of currents, a damped sectional network having a pluralityof diiferent natural periods adapted to be supplied by said source, andan output circuit for said network containing a filter for limiting theoutput of said network to currents of frequencies corresponding to thenatural periods thereof.

16. In a system for generating noise currents, the combination of asource 0 low frequency currents, a sectional loaded artificial lineadapted to be supplied thereby, each of the sections of said linecomprising inductance, capacity and resistance, and an output circuitfor said network containing a filter for extinguishing currents of thefrequency of the low frequency source.

1 A signaling system comprising a source oftele honiospeech frequencycurrents, means or superposing thereon con- I fusion currents of speechfrequency and transmitting them simultaneously with said telephoniccurrents, and means forsubstantially uniformly receiving a band of saidtelephonic currents covering a range of over fifty cycles per secondfree from confusion currents.

18. A signaling system comprising a source of telephonic speechfrequency currents, means for superposing thereon and transmittingsimultaneously therewith confusion currents having several frequencieswithin the speech frequency range for confusing the'signal to betransmitted, means for transmitting a band of over fifty cycles persecond inwidth of said waves with ap- 20. In a signaling system, thec'ombina-,

- tion of a source of signal currents, means for supplying confusioncurrents for confusin the signal to be transmitted, means inclu ingphase regulating means for supplying other confusion currents ofopposite phase to said first mentioned confusion currents, means adaptedto combine the resaid ceived confused signal with said confusioncurrents of opposite phase for clarifying the signal at a distantstation, and means for translating the clarified signal.

21. In a signaling system, the combination of means forsupplyingoscillations, a line, a. pair of current paths adapted to connect saidsupplying means to said line, one of said paths comprising a source forproducing confusion current having a characterist1c frequency componentdependent on a frequency characteristic of said oscillations and anothercharacteristic frequency component independent thereof, and means forpreventing the other of said paths from sending current through said onepath.

22. In asignaling system, the combination of means for supplyingoscillations, a line, a pair of current paths adapted to connect saidsupplying means to saidline, one of said paths comprising means forproducing confusion current together with means for regulating saidconfusion current, and a unidirectionally conducting device in one ofsaid paths for preventing the other of said paths from sending currentthrough said one path.

23. In a signaling system, the combination of means for supplyingoscillations, a line,

a pair of current paths adapted to connect said supplying means to saidline, one of said paths comprising means for roducing currents ofaudible frequency ans a space dischar e device in each of said paths,said device fiaving an input circuit connected to a grid and a cathode,and an output circuit connected to a cathode and an anode, wherebycurrent is unilaterally conducted from said supplying means through saidpaths to line. 24. The combination of means for supplying variablecurrents and a plurality of circuits ada ted to be energized by saidmeans, each of said circuits comprising an oscillation network having aplurality of modes of natural vibration, and means for adjusting therelative phase of the currents supplied to said circui 25. In asignaling system, the combination of a source of signal currents, meansfor supplying confusion current for confusing the signal to betransmitted, means for supplying other confusion currents of oppositephase to said first mentioned confusion currents, a phase adjuster formaintaining the phase opposition between the two said confusioncurrents, and means for translating said signal currents'free fromconfusion.

26. In a signaling system, the combination of a source of signalcurrents, means for supplyingv confusion currents for confusing thesignal to be transmitted, means for supplying other confusion currentsof opposite phase to said first mentioned confusion currents, and'asource of control oscillations for maintaining the phase oppo sitionbetween the two said confusion currents, and means for translating saidsignal currents free from confusion. I

In a signaling system, the combinat1on of a source of signal currents,means for supplying confusion currents for confusmg the'signal to betransmitted, means for supplying other confusion currents of oppositephase to said first mentioned confusion currents, and a source ofcontrol currents for energizing both of Said supplying means, wherebythe two said confusion currents are maintained in phase opposition,

and means for receiving sald signal currentsfree from confusion.

28. In a, receiving system, the combination of an incoming conductor forsupplying a confused wave having a signal component and a confusioncomponent, with signal clarifying means for deriving from energyincoming over said conductor a neutralizing wave and appl ing it to theconfused wave, and means or causing a characteristic of the neutralizingwave to vary in response to changes in a characteristic of the confusedwave.

29. The combination of an incomin line for supplying control currents,CODIfilSlOn currents and signal currents, an outgoing line for supplyinga clarified signal, a pair of current aths connecting said lines, one ofsaid pat s comprising means for Selectively transmitting the signal andconfusion currents, the other of said paths comprising means forderiving, rents, confusion currents of opposite phase to said firstmentioned confusion currents and means for selectively transmitting saidconfusion currents of opposite phase.

30. The combination of an incomin line for supplying control currents,con sion cu rents and s gnal currents, an outgoing from said controlcurline for sup lying a clarified si al, a pair of unilatera lyconducting amp ifying current paths connecting said lines, one of saidconfusion currents of opposite phase.

31. A secret signaling system comprising.

a source of control oscillations, means. for derivin confusion currentsfrom said control oscillatlons, a source of signal currents,

a line adapted to be supplied by said condevice.

trol oscillations and by said signal and said confusion'currents, meansat a receiving stationfor selectively receiving said controloscillations and for deriving therefrom confusion currents of oppositephase to, sald first mentioned confusion currents, and a translatingcircuit in which said signal and said confusion currents supplied tosaid line are adapted to be combined with the confusion currents ofopposite phase whereby signals may be received free from confusion. i

32. A telephone si aling system comprising means for pro ucing speechcurrents and means for producing confusion currents, a means which isoperative in the ab sence of confusion currents for transmitting speechcurrents, means for superposing the confusion currents on the-speechcurrents, and means for receiving speech currents free from theconfusion currents, said -last mentioned means comprising a plurality ofse.

lective energy transferring channels terminating at a commonsignaltranslating 33. In a signaling system, a enerator of sustainedwaves, a modulating evice, a plurality of circuits connecting saidgenerator and said modulating device and translating devices ofdiflerent character in said conne ting'circuits respectively, wherebyelectric l waves of one characteristic are supplied through one of saidcircuits -to 'said modulator during the operation of said generator, andof a different characteristic through the other of'said circuits.

34 The method of wave transmission which comprises receiving electricalwave energy of two kinds, having distinctive freqllilencycharacteristics, at a receiving station, 0 anging the phase of one ofsaid kinds of waves to a predetermined relationship with respect to theother thereof, deriving current energies from said waves of changedphase and other waves, and combining the energles. 35. The'method ofsynchronously product mg two wave energies at a receiving station whichcomprises producing a controlenergy verting them to imposed variations,and receiving said sound wave signaling variations free fromconfusionvariations.

37. The method of radio telephony which consists in radiating signalingcurrent energy in the form of high frequency waves modified inaccordance with signaling variations and confusion variations of thesame general frequency range and at a receiver detectin the highfrequency waves, and selective y entinguishing the confusion variations.

38. The method of telephony which comprises'receiving incoming signalwave energy, transmitting art of the received energy through one patlito an indicating device, transmitting another part of'the received 1energy through another path to the same indicating device, and changingthe frequency of the energy traversing one of said paths.

39,. The method which comprises generating a control wave at onestation, utilizing part of the control wave energy for transmission to acooperatin station, and causing energy of said contro wave frequency tosynchronously generate other waves at each of said stations. v n

40. A transmission system comprising two co-operating stations, meansfor generating a control wave of a given frequency at one of saidstations, means for simultaneously producing energy of the controlfrequency at the other station, and .means vi lhereby said control waveenergy controls t e simi ar waves having a frequency other than thefrequency of the control wave,

generation at each of said stations of- 41. The method of radioreception which comprises successively utilizing at oneostation theenergy of received waves to produce other waves of different frequency,increasing the frequency in at least one instance, and selectin afrequency component of the energy pro uced b each frequency changeincludin the se ection of the energy of increase frequency in at leastone instance of frequency lncrease.

' 42. The method of radio reception which comprises receivin waves,successively connally produce waves of lower frequencies, filtering-saidwaves of lower frequencies by freely transferring a Ill relatively wideband offrequency comporelatively Wide band of Waves of the proin ducedfrequencies having frequencies below a definite frequency andattenuating accompanying waves of all higher frequencies.

In Witness whereof, I hereunto subscribe y A. D., 1921.

Joint MILLS.

name this 22nd day of December 15

